Methods for cleaning turbid nematode suspensions collected from different land-use types and soil types

Soil nematodes are useful ecological indicators and can be extracted from soil by a variety of techniques. Because the extracted nematode samples (suspensions) can be quite turbid (i.e., they contain soil particles and organic particles in addition to nematodes), quantitative and taxonomic analyses of the nematodes by microscopy can be difficult. In this study, the following three methods for cleaning turbid suspensions obtained from Baermann funnels were assessed: repeated centrifugation at 692.5 ×g for 1 min, repeated settling at low-temperature (4°C) for 24 h, and a combination of low-temperature settling and centrifugation. Nematodes were extracted with Baermann funnels from soil samples collected from four land-use types (since land-use type can affect the turbidity of nematode suspensions), and the resulting suspensions were cleaned by the three methods before nematode abundance was assessed. As a control, samples (i.e., suspensions) were simply diluted with water, and nematodes were counted in the entire volume. The results showed that, within each land-use type, nematode abundance did not significantly differ between the control and the three cleaning methods. Averaged across all land-use types, however, the nematode recovery rate was slightly higher with repeated centrifugation than with the other two cleaning methods. Therefore, the proposed methods are sound for cleaning turbid nematode suspensions, and repeated centrifugation is the most efficient method.